The performance of a storage system can be improved with the addition of a cache. Flash caches such as solid-state drives (SSDs) can be incorporated into storage systems and can be quite large. Data stored in the cache is accessed using a cache index, which identifies the location of data in the cache. Because the flash cache may be large, the cache index may need to be stored in the flash cache itself because the cache index may be too large to fit in memory (e.g., RAM).
When the cache index is stored in the flash cache, accessing data in the flash cache becomes more expensive at least in terms of I/O operations. Because the cache index is stored in the flash cache, accessing the cache index is equivalent to accessing the flash cache. The number of I/O operations to the flash therefore increase because any request to access data stored in the cache usually requires that the cache index be accessed first. If each data access requires a corresponding cache index lookup, the flash cache is effectively accessed at least twice for each read operation. Even though a flash cache can be fast, the response time of the flash cache is affected.
In general, there are various operations in which it is necessary to access the cache index or perform a cache index lookup. Read, write, and inquiry operations are examples of operations that are associated with cache index lookups. In addition, cache index updates are also expensive operations at least in terms of I/O, and also in terms of media longevity, because a cache index update requires both an erasure operation and a write operation. Systems and methods are needed to improve the performance of a flash cache and to reduce or minimize cache index lookup operations.